One thing i forgot to ask was what elevation is the 66 gram weights for? I have been testing in 6-8000 feet.
In theory, less primary weight will have less pull or squeeze on the belt. I do understand that the softer secondary spring will make up for that difference. However, leaving the stiffer primary spring will again offset that difference. Again, in theory it will hit a limit to how much it can shift due to the lighter weights and stiff primary spring. I would think that it would be more efficient to go to a 120-310 or 120-300 to allow the lighter weights to have adequate pull at full RPM.